Missouri health officials said Monday they expect reported cyclospora infections to continue climbing as they track a growing outbreak that has now sickened more than 200 people in the state.
During a briefing Monday, state health officials said they are confident the number of reported cases reflects exposure to contaminated food distributed in Missouri, rather than people primarily bringing the parasite back from travel. Investigators are still working to identify the source of the outbreak.
"I know we have a lot of cases of cyclosporiasis, and much more than normal," said DHSS Assistant Communicable Disease Control and Prevention Chief Nathan Koffarnus during a press call on Monday. "It's been growing very rapidly, both here in Missouri and in a lot of places."
While it's normal for a small number of people to test positive for cyclosporiasis during the summer months, St. Louis County Senior Epidemiologist Amanda Brzozowski said this outbreak stands out.
"It is a seasonal infection that does tend to be outbreak-associated," she said. "[But] this is the biggest one I've seen since I've been here for 10 years."
Cyclosporiasis is an intestinal illness caused by the microscopic cyclospora. People typically become infected after eating food containing the parasite, often through produce exposed to contaminated water. Thousands of cases have been reported nationwide this year, with many concentrated in Michigan, Illinois and several other states, including Missouri.
Here's what we know about cyclospora infections in Missouri:
How many people in Missouri have gotten sick? Do we know where they live?
As of Sunday, DHSS had tallied 216 positive cases of cyclosporiasis during the 2026 season. The number is certain to go up as the agency investigates other people who have gotten sick.
The St. Louis County Department of Public Health and the St. Louis Department of Health has logged 57 cases and 10 cases, respectively. Like the state, the departments are updating numbers as they receive more reports of more positive cases.
The state usually logs about a dozen or so cases of the parasitic illness each year.
It's also likely that increased media attention is causing more people to seek testing, which further drives up case counts, Brzozowski said.
"We are seeing a legitimate increase in people who are getting sick," she said. "[But] now they're going to the doctor to find out if their diarrhea is being caused by cyclospora. And the interesting thing is we're not only getting an increase in cyclospora, but we're also seeing an increase in other GI illnesses like campylobacter or salmonella."
Although local health departments sometimes publicize how many people are sickened with the illness, DHSS does not specify where patients who have tested positive live.
Why are different agencies reporting different numbers of positive cases?
It may be confusing to see fewer Missouri cases on the Centers for Disease Control and Prevention's surveillance site than state and local health officials are reporting. In short, it's because of how health departments report cases and how often those numbers are collected and updated.
Typically, local health departments report cases to state health departments, which supply numbers to the CDC and other federal departments. Those systems are not always updated at the same time.
In the meantime, health workers are interviewing patients, asking what food they ate, when they ate it and where they bought it. The interview process for tracing the source of a cyclospora infection can take a half-hour, Koffarnus said.
"There's an additional 15-page interview tool that we use to interview those cases and collect more information," he explained. "That diagnostic tool is kind of how we really drill down on specific products and suppliers and restaurants and things. That's all happening behind the scenes."
Complicating everything is cyclospora's incubation period. It can be days or even weeks before a person who has contracted the parasite begins to show symptoms.
"At the end of the day, we're really just trying to contribute the best information we can here in Missouri, and it's part of a much larger picture across the country," Koffarnus said.
Finally, the federal government is only logging cases that were contracted in the U.S. If someone reports they have returned from a trip abroad, it's not likely they'll be included in the total federal outbreak count.
Where is this parasite coming from?
The Food and Drug Administration said Monday the agency remains focused on lettuce from Taylor Farms in Mexico as the most likely source of the outbreak.
Late last week, representatives from the FDA said their investigation had led them to Taylor Farms. People had gotten sick after eating Taylor-supplied lettuce at Taco Bell locations in five states. That list did not include Missouri. Taco Bell officials say the stores have removed the offending products.
However, soon after, Taylor Farms announced it was voluntarily recalling lettuce products from central Mexico that had been sold in dozens of states, including Missouri. That includes shredded lettuce sold under the Marketside brand at Walmart and other lettuce that was supplied to food service companies nationwide.
But on Sunday, the FDA said a false positive test result had linked the outbreak to the company.
On Monday morning, the regulatory agency posted on its X account that there's still "overwhelming" data that shredded lettuce from the Taylor Farms in central Mexico is the source of the contamination. The voluntary recall of the lettuce is still in effect.
Taylor may sound familiar to some in St. Louis — lawsuits have linked the supplier to an E. coli outbreak that sickened more than 100 people in the region during a 2024 outbreak. The company denies it is the culprit.
Brzozowski said she's confident that the offending food is being sold in the region.
"When we're seeing cases, particularly large number of cases, that means that whatever the source of this outbreak is tends to be widespread and distributed widely throughout the country and certainly throughout our area," she said. "until we completely identify all of the food sources that may be contaminated, and those food sources become removed from the food supply, we will continue to see new cases."
It's possible there may be more than one source of the contamination, officials said.
"We always would love to find the smoking gun with one of these investigations, and I think that's still possible that that'll happen," Koffarnus said.
How can I stay safe?
Health officials say that most people recover from cyclospora infections on their own without treatment. For those who are immunocompromised or who have particularly nasty symptoms, an antibiotic can help clear the infection.
Some people may want to completely avoid produce all together or only eat produce – such as oranges, bananas or avocados – that have peels that are removed before eating.
The best advice is familiar and effective: Wash produce before you eat it.
"Make sure you wash your produce that you buy straight from the grocery store," said St. Louis Health Commissioner Victoria Anwuri. "If you're buying prepackaged produce, like lettuce in a bag, even though it says prewashed, we are encouraging residents to rewash the lettuce."
If in doubt, avoid eating lettuce for a while, she said.
Cooking produce also kills the parasite. For those who really, really love their kale Caesar and other salads, buying leafy greens from a local producer may be a great option. The fewer steps between growing and eating, the better.
"If you are able to identify those steps, if produce is grown locally as opposed to internationally or far away, if it doesn't have to be transported, all of those would make it a safer choice for somebody," Brzozowski said.
What happens if I get sick? Should I go to the doctor?
"It's always helpful for us to know when people test positive for something," Brzozowski said. "But the thing is, most people who get this illness recover without treatment."
In other words, a bit of diarrhea alone shouldn't necessarily prompt someone to go to the doctor.
People should call their doctor if symptoms last for more than a few days, Anwuri said. Those with particularly nasty symptoms may need an antibiotic or an IV to replenish fluids they lost.
"Anyone who's having repeat diarrhea for weeks on end, maybe even two weeks ... if it's continuous, there is concern there, and people should visit their health care provider," she said.
Children may be at higher risk of serious dehydration, she said.
"If it's repeating and coming back, and coming and going back, and then also with significant cramps and body fatigue, that's a sign that it's more than just a normal diarrhea that someone may experience," Anwuri said.
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